The present invention relates to a magnetic separator in general and more particularly, to a magnetic separator for dry and wet material containing magnetically attractable particles.
It is already known to provide a magnetic separator having an upright hollow jacket provided with an upwardly directed inlet and a downwardly directed outlet, and a magnetic system supported on a support so as to be concentric to the jacket. It is also already known to provide such a magnetic system with a plurality of magnet disks and a plurality of pole disks alternating with the magnet disks in the axial direction of the jacket. In such an arrangement, the material to be separated, that is, the material containing magnetically attractable particles, is introduced into the hollow jacket, more specifically into an annular space defined by the jacket and the magnetic system, so that the magnetically attractable particles are attracted to the pole disks during the passage of the material through the annular space from the inlet to the outlet of the jacket. This, of course, results in accumulation of the magnetically attractable particles on the pole disks, so that the magnetic system has to be periodically removed from the jacket for cleaning purposes. In order to facilitate the removal operation, the support supporting the magnetic system may be attached to a door hinged to the hollow jacket. Once the magnetic system is removed from the hollow jacket, the cleaning operation is conducted in a conventional manner, such as manually by cleaning brushes or similar devices, or by blasting.
There is also already known a somewhat different magnetic separator of the above type, in which the mangetic system is also arranged concentrically in an upright hollow jacket having an upper inlet portion and a lower outlet portion, the magnetic system being of the type described above having pluralities of pole and magnet disks alternating in the axial direction of the jacket. In this magnetic separator, however, the cleaning operation is conducted automatically, in that a rotating drum is interposed between the pole disks and the hollow jacket and the material to be separated is introduced between the stationary hollow jacket and the rotating drum with attendant attraction of the magnetically attractable particles to the outer surface of the drum. In this arrangement, the magnetic system is stationary and the pole disks thereof are each provided with a recessed portion so that the magnetic field attracting the magnetically attractable particles to the outer surface of the drum is attenuated whenever a particular portion of the drum reaches the region of the recessed portions. As a result of the weakened magnetic field, the magnetically attractable particles which have been attracted to the outer surface of the drum in the region where the magnetic field is strong, are released from the surface in the region of where the magnetic field is weak and fall into a receptacle for magnetically attractable particles. The efficiency of removal of these particles may be further enhanced if a stationary brush is located in the region of the weakened magnetic field and contacts the outer surface of the drum, removing therefrom those magnetically attractable particles which remain at the surface despite the attenuation of the magnetic field. It is evident that such an automatic removal of the magnetically attractable particles is considerably more advantageous than the manual removal thereof.
In this latter arrangement, the magnetically attractable particles which have been attracted to the outer surface of the drum share the movement of the latter until they are released from or brushed off the surface. While this sharing of movement may be advantageous in some magnetic separators, particularly in such separators which are designed for handling materials having distinct magnetically attractable and magnetically not attractable particles, experience has shown that this arrangement does not achieve the desired results whereever the magnetically attractable and not attractable particles have a certain degree of coherence to each other, such as in wet materials or in materials tending to form agglomerations. In this event, the magnetically attractable particles which are attracted to the rotating surface carry along with them to the region of their removal into the receptacle those not magnetically attractable particles hich adhere to them by mechanical bonds, so that the magnetically attractable material received into the receptacle has less than the desired or attainable purity. This, of course, is very undesirable, particularly in view of the present day requirements for purest possible materials and of the difficulties encountered when such magnetically not attractable particles are to be separated from the magnetically attractable particles in a subsequent separation operation.